Ink drop writing system with nozzle drive frequency control

ABSTRACT

In an apparatus of the type wherein ink under pressure is applied to a nozzle which is vibrated, and the ink emitted by the nozzle thereafter breaks down into ink drops which are charged in a charging tunnel in response to video signals, an arrangement for establishing the nozzle vibration frequency to be a function of the video signals&#39;&#39; frequency and the shape of the video signals.

United States Patent 119 1111 3,736,593

Keur et al. [4 1 May 29, 1973 [54] INK DROP WRITING SYSTEM WITH [56]References Cited NOZZLE DRIVE FREQUENCY UNITED STATES PATENTS CONTROL3,373,437 3/1968 Sweet et al. ..346/75 [75] Inventors: Robert I. Keur,Niles; Henry A.

Dahl, Mount Prospect, both of Ill. Primary Exammer JPseph i a Att0meySamuel Lindenberg, Abraham Wasserman, [73] Ass1gnee: A. B. Dick Company,Ch1cago, Ill. Leon Rosen at F 2 [22] iled Oct 12, 1971 ABSTRACT [21]Appl' 187976 In an apparatus of the type wherein ink under pressure isapplied to a nozzle which is vibrated, and the ink 52 US. Cl ..346/75emitted y the nozzle thereafter breaks down into ink 51 Int. Cl. ..G0ld15/18 l which are charged in a charging tunnel in [58] response to videosignals, an arrangement for F l f Search 346/75 317/3 establishing thenozzle vibration frequency to be a function of the video signalsfrequency and the shape of the video signals.

8 Claims, 3 Drawing Figures DROP FQEQ. DEC FIELD 4o 516NAL S soulzcesougce 51A 32 L 2C0 50 IO d 24 25 NK 1 l2) 2o {22 g aeseavowz 8 17:;

TQANSDUCEQ CHAQQ-HNQI TUNNEL WAST 36 Qset2voil2 INK DROP WRITING SYSTEMWITH NOZZLE DRIVE FREQUENCY CONTROL 7 BACKGROUND OF THE INVENTION 1.Field of the Invention This invention relates to apparatus for writingwith ink drops which are charged by a video signal and directed throughan electric field to be deflected in accordance with the charge, andmore particularly to improvements therein.

2. Description of the Prior Art An ink drop writing apparatus has beendeveloped wherein ink is applied under pressure to a nozzle. The

. nozzle is vibrated or driven in response to synchronizing signals,provided at a selected nozzle drive frequency. The vibrated nozzlecauses an ink jet, which is emitted therefrom to break up into uniformdrops at a distance away from the tip of the nozzle. The rate of suchdrop formation is determined by the vibration rate. A means for chargingeach drop is provided at the location at which the ink stream begins tobreak into drops. This means usually is a conductive tube or cylinder.Video signals are applied between the nozzle and the cylinder inresponse to which a drop assumes a charge determined by the amplitude ofthe'video signal at the time that the drop breaks away from the jetstream.

The drop thereafter passes through a fixed electric field, as a resultof which it is deflected by an amount determined by the amplitude of thecharge on the drop.

At the boundary of the electric field there is positioned a writingmedium upon which the drop falls. Since the deflection of the drop isdetermined by the charge on the drop, the arrangement enables one towrite information with the ink which is carried by the video signal.

As previously stated, at the time that a drop separates from the fluidstream, the drops are charged by electrostatic induction. If the fieldestablished by the video signal is maintained while the drop separates,the drop will carry a charge determined by this video signal. Obviously,if the video signal is in the process of rising or falling or is notpresent at the time the drops separate, the charge on the drop will notbe that of the video signal. In order to place specific charges on givendrops, one must known when drop separation is occurring or the phasingof the drop formation relative to the video signal. In the absence ofcontrol over drop separation time, because of unpredictable phasechanges in the ink drop formation, the uniformity and the fidelity ofthe printing are affected adversely.

Various systems have been proposed and designed to control drop phasingin order to improve the printing of such ink drop writing devices. Twosuch systems are described in U. S. Pat. Nos. 3,465,351 and 3,562,761.None of the prior art systems control drop phasing on the basis of theshape of the video signals on which the probability of proper dropcharging greatly depends.

OBJECTS AND SUMMARY OF THE INVENTION in an ink drop writing system anovel arrangement for controlling the nozzle drive frequency so as tomaximize the probability of proper drop charging.

These and other objects of the present invention are achieved byproviding in an ink drop writing system an arrangement which establishesthe nozzle drive at a frequency, i.e., the frequency at which the nozzlevibrates, to be a function of the frequency of the video signals, aswell as the shape of such signals.

The novel features of the invention are set forth with particularlity inthe appended claims. The invention will best be understood from thefollowing description when read in conjunction with the accompanyingdrawings.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a block diagram of a typicalprior art ink drop writing system;

FIG. 2 is a diagram of a single video signal; and

FIG. 3 is a block diagram of one embodiment of an ink drop writingsystem in accordance with the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a schematic drawingof thepresently known arrangement which is shown to afford a betterunderstanding of the invention. An ink reservoir 10 provides ink underpressure'to tubing 12 which is flexible. An electromechanical transducer14 is usually placed adjacent to or around the tubing. The transducer isdriven in response to signals from a source 16. The transducer serves tovibrate and/or compress the tubing 12 in the region of the nozzle 18.This results in an ink jet 20 being emitted which at a short distancedownstream breaks up into drops 22 which are formed at a rate determinedby the frequency of the vibration. In the re- 'gion where the stream 20breaks down into drops, a charging tunnel 24 is provided. This comprisesa conductive cylinder to which video signals from a video signal source26 are applied. The video signals establish a field within the chargingtunnel so that the ink drops which are formed therein assume a chargedetermined by the amplitude of the video signal present at the time thedrop separates from the ink jet 20.

Downstream of the charging tunnel there are usually placed a pair ofelectrodes 28 which are connected to a field bias source 30. As aresult, there is established between the electrodes a constant electricfield. The ink drops, which bear charges in accordance with the videosignal, enter this field and are deflected by an amount which isproportional to the amplitude of the charge. This enables intelligentwriting to occur on a writing medium 32, which is moved at somesynchronous rate past the electrodes. Drops which do not bear a videocharge are captured by a tube or trough 34 which is'judiciouslylplacedat one side so as to capture these drops. It leads to a waste reservoir36. The paper 32 moves into the plane of the drawing whereby its motion,together with the deflection of the drops, may be used for formingintelligible characters.

As previously stated intelligible characters can only be formed if thedrops are properly charged, which is achievable only with proper dropphasing. Alternately stated, proper drop charging can be achieved onlywhen the frequencies of the video signals and the nozzle vibration ordrive are in a proper relationship. In accordance with the presentinvention, unlike prior art systems, the nozzle drive frequency ischosen as a function of the video signals frequency, hereafterdesignated F,,, and the shape of such signals.

FIG. 2 to which reference is now made is a waveform diagram of a singlevideo signal or pulse, the abscissa designating time and the ordinateamplitude or level in terms of volts. Each signal comprises an intervalT during which the signal amplitude is at an established level,designated by line 40. The interval or time T is preceded and followedby a'signal rise time T, and a signal fall time T,, respectively. Thevideo period equalling T,+T is defined as T, and the total signal timeis defined as T The number of video periods T, per second is defined asthe video frequency and is designated as F,.

In accordance with the present invention the nozzle is driven at afrequency, hereafter referred to as the drop frequency and designated Fsomewhat different than the video frequency F This frequency differencehas been found to prevent the system from being set in an improper phaseor bad phase condition for long periods of time, which if permitted tooccur would result in unacceptable performance. It has been discoveredthat no more than one error on adjacent video pulses occurs if one ofthe following relationships is maintained:

F as expressed in equation (2), is higher than F,. It

represents a drop period equal to T If the following relationship isheld:

there will be one or more drops that separate from the stream during Ti.e., the interval of the flat top of the there will be fewer drops thanvideo pulses.

One can think of the drop separations as sampling of the videocondition. If there are fewer samples taken than there are pulses todetect, it is obvious that some pulses will not be displayed asdeflected drops. Then there will be missing spots in the construction ofa character. If there are more samples taken than there are videopulses, there will be extra drops in the construction ofa character butno needed drops will be missing. Based on these considerations it hasbeen determined that near optimum results are achieved when F x T l anda ri/( r)- F 16,500/l 16,500 X 10 16,777 Hz.

In practice F, is a function of the character generation system and thedesired character rate, and therefore is generally fixed. Based on theshape of the video pulses and F,,, F, is determined in accordance withequation (2) and (5).

FIG. 3 to which reference is now made is a diagram of an embodiment ofan ink drop writing system which incorporates the teachings of thepresent invention. Therein elements like those in FIG. 1 are designatedby like numerals. In accordance with the present invention a dropfrequency source 40 which is connected to transducer 14 is incorporated.Source 40 activates the transducer with signals at the drop frequency Fd which, once chosen as herebefore explained, remains constant and isnot changed unless F or the video pulse shape is changed. I

There has accordingly been shown and described herein an improved inkdrop writing system. The improvement over the prior art is realized bythe means for and method of controlling the relative frequencies of thevideo signals and the nozzle vibration to minimize the likelihood ofimproper charging of successive drops. Basically in accordance with thepresent invention the nozzle drive frequency, referred to as the dropfrequency, is made to be a function of the video signal frequency andvideo signal waveshape.

It should be appreciated that various modifications and/or equivalentsmay be substituted for the arrangements as shown without departing fromthe true spirit of the invention. For example, herebefore F d wasdescribed as being a function of T,. This is based on the assumptionthat the rise time T, is greater than the fall time T,, which is typicalof most video pulses. If how ever one were to. use video pulses with afall time greater than the rise time, T, should be substituted for T, inequation (2). Thus in general it may be stated that F,, is a function ofF, and the rise or fall times, whichever is greater. Also herebefore itwas indicated that it is preferable to chose F in accordance withequation (2). In such a case, though extra drops may occur,one insuresagainst any voids in the generated character. Clearly if one or morevoids can be tolerated in the'generated characters, F d can be chosen inaccordance with equation l i.e., F =F l+F,,XT,). Therefore all suchmodifications and equivalents are deemed to fall within the scope of theinvention as defined in the appended claims.

What is claimed is:

1. In an ink drop writing system of the type wherein ink under pressureis delivered to a nozzle, a transducer vibrates the nozzle as a functionof drive signals supplied thereto, the nozzle emits an ink jet whichbreaks up into drops, a charging tunnel is positioned in the region atwhich the ink jet breaks up into the drops, the charging tunnel beingadapted to respond to video signals to charge the drops passingtherethrough as a function of said video signals, the improvementcomprising: video pulse signal source means coupled to said chargingtunnel for applying video signals thereto at a preselected firstfrequency; and nozzle drive means for applying drive signals to saidtransducer at a second frequency to vibrate said nozzle therewith, saidsecond frequency being a function of said first frequency and the riseor fall time of said video pulse signals. 2. The arrangement as recitedin claim 1 wherein said second frequency is higher than said firstfrequency.

3. In a ink drop writing system of the type wherein ink under pressureis delivered to a nozzle, a transducer vibrates the nozzle as a functionof drive signals supplied thereto, the nozzle emits an ink jet whichbreaks up into drops, a charging tunnel is positioned in the region atwhich the ink jet breaks up into the drops, the charging tunnel beingadapted to respond to video signals to charge the drops passingtherethrough as a function of said video signals, the improvementcomprising: video signal source means coupled to said charging tunnelfor applying video signals thereto at a preselected first frequency; andnozzle drive means for applying drive signals to said transducer at asecond frequency to vibrate said nozzle therewith, said second frequencybeing a function of said first frequency and the shape of said videosignals, the duration of each video signal being characterized by afirst time interval during which the level of the signal rises from areference level to a selected level, a second time interval, followingsaid first time interval, during which the signal level is at saidselected level, and a third time interval, following said second timeinterval, during which said signal level falls from said selected levelto said reference level,said first and third time intervals beingdefinable as the rise and fall times of the signal, respectively, saidsecond frequency being a function of at least said'first frequency andsaid rise time.

4. The arrangement as recited in claim 3 wherein F,, F,,/l F, T,, whereF, and F d are the first and second frequencies respectively, and T issaid rise time.

5. The arrangement as recited in claim 3 wherein the second frequency,definable as F is higher than said first frequency, and F -T is not lessthan 1, where T, represents said second time interval.

6. The arrangement as recited in claim 3 wherein F =F,,/( l F,,-T,,),where F and F are the first and second frequencies respectively, and T,is the greater of said rise time and fall time.

7. The arrangement as recited in claim 6 wherein the second frequency, Fd is higher than said first frequency and F -T is not less than 1, whereT is said second time interval.

8. The arrangement as recited in claim 3 wherein F =F,,(1F,,-T,) whereF, and F d are the first and second frequencies respectively, and T, isthe greater of said rise time and fall time.

UNITED STATES PATENT OFFICE 5 v CERTIFICATE OF C( )RREC"1I ON Patent No-3,736,593 f Dated May 299 1973 lnventofls) ROBERT 1'. KEUR, ET; AL. V II It is certi fied that' error appears in the above-identified patentand that said Letters Patent are hereby corrected as shown below:

Column 5, '1ine 45 should read as follows Video pulse. However if; "'1Column 4 line 11, lt he'denomlnator of the fraction" should be enclosed-.in parent'he sis and shou-ld appear as follows: 7 16,5'00/(1-16 ,S0OColumn 6, line 12, thedenominator-10f ti 1e frac-t ion ehoul d be in"parenthesis and should appear as follows:

Signed and sealed this 22nd day: of Jan ua-ry 1-1974;

V SEAL] Att'est': I I

EDWARD M.FLETCHER,JR, "RENE D. TEGTMEYER v a a Att esting. Officer i I,A a tingConirnis eioner of Patents UNITED STATES PATENT OFFICECETIFICATE OF CORRECTION Patent No. 5,736,593 Dated May 29, 1973lnventofls) ROBERT I. KEUR, ET. AL.

It is certified that error appears in the above-identified patent andthat said Letters Patent are hereby corrected as shown below:

Column. 3, line 45 should read as follows: video pulse However if: kColumn 4, line 11, the denominator of the fraction should be enclosed inparenthesis and shou-ld n appear as follows: l6,500/(ll6,500 x 10- jColumn 6, line 12, the denominator of the fraction should be inparenthesis and should appear as follows F l-F T Signed and sealed this22nd "day of January 1974.

(S A Attest:

EDWARD M.PL ETCHE R,JR. RENE D. TEGTMEYER Attesting Officer ActingCommissioner of Patents

1. In an ink drop writing system of the type wherein ink under pressureis delivered to a nozzle, a transducer vibrates the nozzle as a functionof drive signals supplied thereto, the nozzle emits an ink jet whichbreaks up into drops, a charging tunnel is positioned in the region atwhich the ink jet breaks up into the drops, the charging tunnel beingadapted to respond to video signals to charge the drops passingtherethrough as a function of said video signals, the improvementcomprising: video pulse signal source means coupled to said chargingtunnel for applying video signals thereto at a preselected firstfrequency; and nozzle drive means for applying drive signals to saidtransducer at a second frequency to vibrate said nozzle therewith, saidsecond frequency being a function of said first frequency and the riseor fall time of said video pulse signals.
 2. The arrangement as recitedin claim 1 wherein said second frequency is higher than said firstfrequency.
 3. In a ink drop writing system of the type wherein ink underpressure is delivered to a nozzle, a transducer vibrates the nozzle as afunction of drive signals supplied thereto, the nozzle emits an ink jetwhich breaks up into drops, a charging tunnel is positioned in theregion at which the ink jet breaks up into the drops, the chargingtunnel being adapted to respond to video signals to charge the dropspassing therethrough as a function of said video signals, theimprovement comprising: video signal source means coupled to saidcharging tunnel for applying video signals thereto at a preselectedfirst frequency; and nozzle drive means for applying drive signals tosaid transducer at a second frequency to vibrate said nozzle therewith,said second frequency being a function of said first frequency and theshape of said video signals, the duration of each video signal beingcharacterized by a first time interval during which the level of thesignal rises from a reference level to a selected level, a second timeinterval, following said first time interval, during which the signallevel is at said selected level, and a third time interval, followingsaid second time interval, during which said signal level falls fromsaid selected level to said reference level, said first and third timeintervals being definable as the rise and fall times of the signal,respectivEly, said second frequency being a function of at least saidfirst frequency and said rise time.
 4. The arrangement as recited inclaim 3 wherein Fd Fv/1 - Fv Tr, where Fv and Fd are the first andsecond frequencies respectively, and Tr is said rise time.
 5. Thearrangement as recited in claim 3 wherein the second frequency,definable as Fd is higher than said first frequency, and Fd.Te is notless than 1, where Te represents said second time interval.
 6. Thearrangement as recited in claim 3 wherein Fd Fv/(1-Fv.Tx), where Fv andFd are the first and second frequencies respectively, and Tx is thegreater of said rise time and fall time.
 7. The arrangement as recitedin claim 6 wherein the second frequency, Fd is higher than said firstfrequency and Fd.Te is not less than 1, where Te is said second timeinterval.
 8. The arrangement as recited in claim 3 wherein FdFv(1-Fv.Tx) where Fv and Fd are the first and second frequenciesrespectively, and Tx is the greater of said rise time and fall time.